The value of anti-lock braking has been recognized for a number of years, and systems providing that function have been developed and operated successfully, especially in the more sophisticated and expensive lines of vehicles. Their use is widespread enough for them to be known by the acronym "ABS", but despite their proven merit as safety devices, they are not yet in general use. Part of the reason for this situation is the cost of fabrication and installation. Also, of course, reliability of the ABS must be of a high order in an accessory involved in the vital action of vehicular braking, which means that components tend to be relatively expensive.
Almost all anti-lock brake systems, particularly those for automotive use, are involved with hydraulic brakes. Basic hydraulic brakes include reservoir of brake fluid which connects to or forms a part of a master cylinder in which a piston is reciprocally movable by means of a foot pedal. The master cylinder is connected by hydraulic fluid tubes to a slave cylinder at each wheel of the vehicle. Each slave cylinder also has a reciprocally movable piston mechanically connected to move a brake shoe against a drum or a brake caliper against a disk.
Skidding takes place when the vehicle operator presses the pedal which applies the brakes and a wheel or wheels become locked against rotation and slide uncontrollably on a slippery surface. Anti-lock brake systems (ABS) are designed to sense such locking and quickly and momentarily release the locked wheel. A lock-and-release cycle should then take place rapidly and repetitively, permitting very short pulses of angular wheel rotation. Thus, skidding episodes are disrupted as the wheel resumes rotating rather than locking and sliding.
Typically, a sensor detects decelerating rotation or a locked wheel and triggers an ABS electronic control module which shifts the appropriate ABS valve to discontinue further fluid transfer to the wheel cylinder. Also, the ABS valve is switched to tap off hydraulic fluid from the wheel cylinders. Fluid that is so tapped off is collected in an auxiliary ABS reservoir. The wheel cylinder being thus depressurized, the brake releases and the wheel can again rotate. To keep the whole system continuously operative, enough fluid must be returned to the master cylinder reservoir to prevent it becoming fully depleted. This function is served by a pump timed in operation by the ABS control in conjunction with the tapping off of fluid from the wheel cylinders
To that end, a linkage including a reciprocal plunger is employed between the vehicle's brake pedal and a switch which is also connected to the ABS control along with the rotation sensor. A balance must be achieved between operator foot pressure applied to the brake pedal and back pressure applied in opposition by the master cylinder piston being moved in response to fluid coming from the pump During an ABS stop, the pedal actually dithers about the point in its travel at which switching occurs.
Different vehicular specifications and even normal manufacturing tolerances demand that the linkage between the pedal and the ABS switch be adjustable in length to accommodate differing amounts of pedal travel. Adjustment must also permit the matching of the pedal free (retracted) position with limit of extension of the plunger from the switch body. Limiting of the pedal excursion by the ABS switch itself is to be avoided. It is with practical solutions of these problems that the present invention is concerned and has for its primary objects.
Another object is making possible more general use of ABS braking systems through reduction of cost of parts, fabrication and installation.
A further object is the simplification of installation and the prevention of faulty installation of ABS braking in vehicles.
For a better understanding of these and other objects, features, and advantages of the present invention, reference should be made to the following description of a preferred embodiment which should be read in conjunction with the appended drawing in which: